The present invention relates to a method of reinforcing a grassed surface layer, primarily for a sports ground such as a horse race track, athletics field or football pitch, although surfaces for any suitable sports can be reinforced using the invention.
A particular problem with sports grounds is that the surface should not be too hard, but good drainage is required and muddy or clayey surfaces are undesirable. Furthermore, public and performers' preference is for a natural grassed surface. From the point of view of drainage, sand performs well, but it is not very coherent, even when grassed, and the surface is easily damaged. One possible solution would be to place a layer of mesh structure just below the surface, but in practice this is highly unsatisfactory. If the mesh structure layer is firmly anchored, players can be badly injured, for example if a boot stud catches in a mesh; if the mesh structure is not firmly anchored, large pieces of mesh structure can be lifted out.
It is already known to use a plastics material mesh structure layer in order to form coherent sods for laying lawns or golf courses--see U.S. Pat. Nos. 2,605,589, 3,863,388, 3,845,584 and 3,980,029, and also the film entitled "World of Netlon" as well as a leaflet entitled "Netlon Bravura Turf" and a booklet entitled "Netlon Bravura Turf". It is also practised with Bermuda Grass (in particular) that the grass, once laid, is slit in one direction in order to cut the transversely growing stems and encourage additional growth. The slits are continuous, and normally about two inches apart. There is also another known procedure in which relatively small elements of open plastic mesh are randomly mixed with soil in order to increase the load-bearing capacity of the soil. Such a procedure is described in GB-A-2 120 475, and is also referred to in the booklet "Netlon Mesh Elements--a Case History", describing the use of the mesh elements at the Sha Tin Race Course in Hong Kong--in the latter disclosure, there is a reference to slitting the grass, as already described above in relation to Bermuda Grass.
None of the above disclosures has solved the problem with which the present invention is concerned.